The present invention relates to a process for treating a radioactive liquid waste which can bring about an approximately complete recovery of uranium and .beta.-decay nuclids, daughter nuclides of uranium, from a radioactive liquid waste containing these radioactive materials and a remarkable reduction of the radioactivities of a final drain.
A process liquid waste discharged from the uranium hexafluoride reconversion process contains 50-200 ppm of uranium and a very small amount of .beta.-decay nuclides, daughter nuclides of uranium. As a method for removing these radioactive nuclides from the above-mentioned process liquid waste, there have been proposed an ion exchange method, a flocculation method using iron chloride as a fluocculant and the like.
The ion exchange method comprises such processes as shown in FIG. 1. For effective use of ion exchange resins, it is usually required to regenerate the ion exchange resins, for example, about once a day. Therefore, in the continuous treatment of the above-mentioned process liquid waste from the uranium hexafluoride reconversion process, two series of ion exchange treatment lines are required to carry out the regeneration of the ion exchange resins simultaneously. On the other hand, the regeneration of the ion exchange resins requires a large amount of nitric acid, and after regeneration, a waste liquid containing the nitric acid is discharged, consequently a nitric acid recovering equipment is necessary. Further, the ion exchange resins are deteriorated by repeated regeneration. This deterioration of the ion exchange resins is thought to be attributable to 10-20 g/l of fluorine contained in the above-mentioned process liquid waste and the nitric acid used in the regeneration thereof. In addition to these defects, the ion exchange method has the following defect. Namely, the ion exchange method is indeed extremely effective for capturing the uranium contained in the above-mentioned process liquid waste, but when thorium, daughter nuclide of uranium, and uranium coexist in the said liquid waste, complete capture of the thorium by the ion exchange method is difficult owing to a high specific activity of thorium.
The flocculation method using iron chloride as a flocculant comprises such processes as shown FIG. 2. In this method, even though a precipitate capturing uranium in the above-mentioned process liquid waste is formed and the captured uranium is eluted by acid treatment of the precipitate to be recovered, separation of the eluted uranium from iron ions coexisting in large quantities is not easy, consequently the precipitate capturing uranium must be stored as a radioactive solid waste.
Further, in the flocculation method using water glass as a flocculant as disclosed in Japanese Patent Publication No. 38320 of 1973, uranium in the above-mentioned process liquid waste can be almost completely captured by an amorphous silica precipitate formed by addition of water glass, but .beta.-decay nuclides such as thorium, daughter nuclides of uranium, can not necessarily be captured sufficiently and even when the captured radioactive nuclides are recovered from the precipitate, the residual precipitate can not be handled as a nonradioactive waste, consequently the precipitate capturing these radioactive nuclides has been stored intact as a radioactive solid waste.